The present invention relates to a method of producing plastic coated ink rollers for printing presses, by crimping a heated, tubular jacket of a plastic material, such as PVC, onto a metal cylinder.
Today, rollers for printing presses are usually made from stainless steel, or they are mild steel cylinders coated with vinyl or hard rubber. Since such rollers or cylinders are expensive they are not replaced as often as would be recommendable, which frequently leads to an excessive amount of waste at printing start-up.
For several years experiments have been going on with plastic coated steel rollers, because PVC plastic material shows better properties than steel, copper and nylon with respect to the capability of retaining oil-containing ink when water drops are added to the ink in the damping system of the press during printing. It has also been a requirement that the plastic coated rollers should be capable of withstanding machining in a lathe to pattern their surfaces. However, this requirement has not been fulfilled since one has not succeeded in obtaining a sufficiently stable bonding between the plastic and the steel material of the rollers.
Most plastic materials, including PVC, have a thermal coefficient of expansion substantially higher than those of the metals which are used to form the metal cylinder of the printing rollers, such as steel. A method likely to be suitable for making plastic coated ink rollers would be to crimp a heated tubular plastic jacket onto the metal cylinder, the plastic material upon cooling contracting sufficiently to cause a friction bonding to the metal cylinder. However, practice has shown that the metal cylinder, owing to its high thermal conductivity, causes the plastic coating material to cool down at such a high rate that in order to be able to altogether manage to get the plastic coating onto the cylinder the difference between the external diameter of the metal cylinder and the internal diameter of the heated tubular plastic jacket has to be of such a size that the crimping forces, and consequently the friction forces, after cooling will not be sufficient to retain the plastic jacket on the metal cylinder when external stresses are applied to the plastic jacket, such as when machining it in a lathe. therefore some kind of adhesive or other auxiliary means of mechanical type, such as indentions, protrusions or the like, must be utilized to secure the plastic jacket to the metal. This of course will increase the costs of production, and a reliable bonding is not always obtained.